The present invention relates to position data display/control apparatus and methods which use position data received from GPS (Global Positioning System) satellites to display data on the present position.
A GPS is an accurate navigation system which selects at any position on the earth four ones from a plurality of artificial satellites which move around the earth, receives signals from those selected artificial satellites and obtains data on a latitude and longitude of that position on the earth. This GPS constitutes a single built-in navigation aiding apparatus by which an airplane can navigate anywhere in the world and accurate position data is obtained at once, so that the number of airplanes can increase secondarily in one air route, advantageously.
The GPS is further used in each of other fields of navigation of ships/automobiles, control of services of vehicles such as taxis/trucks, map/building measurement, fish finding, leisure activities such as fishing/mountain climbing, study and sciences such as diastrophism, earthquake prediction, etc.
For example, in the navigation of an automobile using a GPS, a present position of the automobile is indicated on a map displayed usually on a display for the user's benefits. Maps in various countries in the world are produced based on respective different techniques for expressing the spherical earth in a plane map, and different geodetic systems different in elements including a central point in making a map. Thus, when a geodetic system is set in the conventional GPS, the user selects a required geodetic system from among preset ones in the whole world, and sets it to correct the position indication accurately. In addition, also when the present position is set to reduce an initial position measuring time, the user inputs data on the latitude and longitude of the user's present position.
As described above, when the latitude and longitude of the user's position measured by the GPSs are adjusted to those of a corresponding position in a map, the user is required to select a required geodetic system from among many preset ones in the whole world and to set it. Thus, the user is required to perform many key-in operations to locate the desired geodetic system, which is a problem to operability of the GPS.
Also, when the user's present position is set to reduce the initial position measuring time, the user is required to input data on the latitude and longitude of the user's present position. Thus, the user is required to beforehand know a rough latitude and longitude of the user's present position and further required to input numerical values of the latitude and longitude one by one, which is also a problem to the operability of the GPS.